The present application claims priority to Japanese Application No. P10-220299 filed Aug. 4, 1998, which application is incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
This invention relates to a semiconductor device manufacturing method particularly suitable for use in fabrication of a thin-film transistor.
2. Description of the Related Arts
In a typical thin-film transistor (TFT), its active region is made of a polycrystalline silicon (Si) film, for example. When manufacturing a thin-film transistor of this type, the polycrystalline Si film is usually hydrogenated to decrease the trap density of crystal grain boundaries of the polycrystalline Si film forming the active region and thereby to improve the performance characteristics of the film transistor. Heretofore, the hydrogenation of the polycrystalline Si film has been done by first making a hydrogen-containing film, such as silicon nitride (SiNx) film containing hydrogen, on a polycrystalline Si film, and then annealing the substrate at a temperature higher than approximately 300xc2x0 C.
On the other hand, plastic substrates of polyether sulfone (PES) and polyethylene terephthalate (PET) have recently become to be used as substrates of thin-film transistors.
However, heat-resistant temperature of plastic substrates of polyether sulfone is about 200xc2x0 C., and heat-resistant temperature of plastic substrates of polyethylene terephthalate is about 100xc2x0 C. Both are lower than heat-resistant temperatures of glass substrates, and they involved the following problem.
That is, for hydrogenation of the polycrystalline Si film, the conventional technology had to heat the substrate to 300xc2x0 C. or higher. When the substrate is a glass substrate, the process is done well. However, when using a plastic substrate of PES or PET having a low heat resistance as explained above, the substrate cannot resist the process temperature. Therefore, processes for manufacturing thin-film transistors need a technique capable of hydrogenating the polycrystalline Si film at a temperature not higher than heat-resistant temperatures of plastic substrates.
It is therefore an object of the invention to provide a manufacturing method of a semiconductor device capable of hydrogenating a semiconductor film without damaging its substrate even when the substrate is of a kind having a low heat resistance like a plastic substrate.
According to the invention, there is provided a semiconductor device manufacturing method comprising the steps of:
forming a semiconductor film on a substrate;
forming a hydrogen-containing film on the semiconductor film; and
irradiating a pulse energy beam to heat the hydrogen-containing film and thereby diffuse hydrogen in the hydrogen-containing film into the semiconductor layer.
In the present invention, a low heat-resistant substrate having a heat-resistant temperature of 300xc2x0 C. or lower, for example can be used as the substrate. Examples of the substrate of this type are plastic substrates of polyether sulfone whose heat-resistant temperature is approximately 200xc2x0 C., plastic substrates of polyethylene terephthalate whose heat resistant temperature is approximately 100xc2x0 C. Further examples are plastic substrates of polymethyl methacrylate (PMMA) and plastic substrates of polycarbonate (PC). Typically used as the semiconductor film is a polycrystalline semiconductor film or a non-single-crystalline semiconductor films such as amorphous semiconductor film. However, a single-crystalline semiconductor film is also usable. More particularly, a polycrystalline silicon film, amorphous silicon film or single-crystalline silicon film, for example, is used as the semiconductor film. Typically used as the hydrogen-containing film is an insulating film containing hydrogen. However, a semiconductor film containing hydrogen is also usable. More particularly, a silicon nitride film or an amorphous silicon film containing hydrogen, for example, is used as the hydrogen-containing film. The pulse energy beam is irradiated from the side of the hydrogen-containing film onto the substrate having formed the hydrogen-containing film.
In the present invention, laser beams are typically used as the pulse energy beams. Other than laser beams, electron beams and ion beams are also usable as the pulse energy beams. The pulse energy beam is irradiated from the side of the hydrogen-containing film, for example, to the substrate having formed the hydrogen-containing film. In this invention, the pulse energy beams preferably have a wavelength absorbed by the hydrogen-containing film to ensure the hydrogen-containing film be effectively heated by irradiation of the pulse energy beams. If the pulse energy beams are not absorbed by the hydrogen-containing film but are absorbed by the underlying semiconductor film, heating of the semiconductor film results in heating the hydrogen-containing film. Therefore, such pulse energy beams can be used as well. Energy density, number of pulses and width of a pulse of the pulse energy beams are preferably determined not to melt the semiconductor film. Alternatively, the semiconductor film may be crystallized and re-crystallized by irradiating other pulse energy beam to the semiconductor film after making the semiconductor film on the substrate and before making the hydrogen-containing film on the semiconductor film. In this case, for example, energy density of the pulse energy beams used for heating the hydrogen-containing film is determined to be lower than the energy density of the other pulse energy beams used to crystallize or re-crystallize the semiconductor film.
According to the invention having the above-summarized construction, since the semiconductor film can be hydrogenated by irradiating the pulse energy beam, thereby heating the hydrogen-containing film, thereby diffusing hydrogen in the hydrogen-containing film into the semiconductor film and thereby selectively heating the hydrogen-containing film, the semiconductor film can be hydrogenated without damaging the substrate even when the substrate is a low heat-resistant substrate like a plastic substrate.
The above, and other, objects, features and advantage of the present invention will become readily apparent from the following detailed description thereof which is to be read in connection with the accompanying drawings.